This invention relates to a rotary feeder and, more particularly, to an improved intercompartment seal for such feeder.
Typical rotary feeders are disclosed in U.S. Pat. Nos. 2,879,094; 2,886,191; 3,052,383 and 3,201,007. In general, a rotor having compartment defining radial walls is mounted within a cylindrical rotor cavity of a housing to rotate between an inlet port and an outlet port that communicate with the cavity. There are two aspects to sealing the compartments -- sealing the interface between the end of the rotor and the cavity and sealing the compartments from each other. They function to transfer particulate materials in a fluid media such as a gas in segments from the inlet port to the outlet port. Conventionally, the intercompartment seals comprise a blade mounted at the end of each radial wall. One technique employs a blade made of a flexible material, such as rubber, in contact with the peripheral surface of the cavity. The flexibility of the material ensures that the blade will remain in contact with the peripheral surface of the cavity despite surface irregularities and axial misalignment of the rotor within the cavity. Materials from which flexible blades are made tend to deteriorate when exposed to extremely high or low temperatures, and to abrasive particulate material. Another technique employs a soft metallic blade that has a chamfered surface in contact with the peripheral surface of the cavity. Metallic blades tend to wear down in use, particularly when the feeder handles abrasive particulate material. Thus, such metallic blades must be frequently readjusted and replaced to maintain contact as they wear in the course of operation.
In a pyrolytic process, a typical application of a rotary feeder is to couple particulate solids separated from a gaseous carrier stream by a cyclone to another gas stream at a higher pressure. If the intercompartment seals do not function effectively, too much gas will flow through the feeder in the reverse direction. This is known as "blow-by". This reverse flow carries with it the separated particles, thereby reducing the efficiency of the transfer operation. Furthermore, the reverse flowing gas mixes with the gas in the cyclone, which is highly objectionable in a process where isolation is a requirement.